Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modern wind turbine typically includes a tower, a generator, a gearbox, a nacelle, and a rotor having one or more rotor blades. In many wind turbines, the rotor is attached to the nacelle and is coupled to the generator through the gearbox. The rotor and the gearbox are mounted on a bedplate support frame located within the nacelle. The rotor blades capture kinetic energy of wind using known airfoil principles. Thus, the rotor blades transmit the kinetic energy in the form of rotational energy so as to turn a shaft coupling the rotor blades to a gearbox, or if a gearbox is not used, directly to a generator shaft of the generator. As such, the gearbox may be used to step up the inherently low rotational speed of the turbine rotor for the generator to efficiently convert mechanical energy to electrical energy, which is provided to a power grid. In addition, a plurality of wind turbines in a common geographical location is generally referred to as a wind farm and can be used to generate electricity for the power grid. The individual wind turbines may each have a turbine controller communicatively coupled to a farm controller that provides supervisory control to the wind farm.
During operation of the wind farm, the power grid may suffer from one or more grid contingency events. As used herein, a “grid contingency event” or similar generally refers to any grid event that may cause a sudden, wide area disturbance or power outage. For example, certain grid contingency events are the result of a loss of a transmission line, fault events, and/or generation failures. During such events, the grid is left in a degraded operating mode where the impedance is generally too high to accommodate the power from the energy source, e.g. the wind turbine generators within the wind farm.
In this instance, the physics of the power grid can lead to a phenomenon generally referred to as “pole-slipping.” Further, weak grid conditions can be particularly prone to pole-slipping. Pole-slipping, which comes from conventional power generation via synchronous machines, occurs when the rotor angle of the machine moves beyond the point where the restraining torque of the power grid can balance the mechanical input to the wind turbine. The result is an increase in turbine speed. In addition, each time the angle relative to the power grid passes through 360 degrees, a pole of the generator “slips” with respect to the power grid. Thus, pole-slipping can have negative consequences, thereby leading to repetitive voltage depressions and/or severe power pulsations on the power grid and/or one or more of the wind turbines in the wind farm. In addition, with a power electronic interface, a similar situation can occur, but at a faster rate than with conventional power generation and can also include overvoltage conditions.
In view of the aforementioned, uncontrolled disconnections of wind turbine generators and transmissions assets are possible. Thus, improved systems and methods for stabilizing wind turbine disconnection during a contingency event of the power grid would be advantageous. Accordingly, the present disclosure is directed to a system and method that disconnects selected wind turbine generators in a wind farm from the power grid to quickly and effectively stabilize the system such that higher-level controls of the remaining wind turbine generators in the wind farm can bring the system to an acceptable and stable condition.